A few things …
First… welcome to the forum.
As for the issues… I read the problem about the PLA+ not sticking and various bed temps … but all that got pushed aside as soon as you mentioned the broken fan shroud and loose heat-block. You’ll need to get those two issues sorted out before worrying about proper bed temps. (For the record, I print PLA using 230°C for the HE 0.5mm head … this is the head that comes with the printer and it is a “hardened” steel hot end capable of dealing with materials and temperatures beyond what many other printers can handle (hence the “Workhorse” name.). LulzBot sells many optional nozzles from 0.25mm for small parts with high detail; 0.5mm in brass vs. hardened steel nozzles; a 0.8mm nozzle with an E3D “volcano” hot-end for printing at higher speeds and good for larger parts, and a 1.2mm nozzle which also uses the E3D “volcano” hot-end for really big parts at really fast speeds. It’s pretty easy to swap the tool-head.
On to your issue…
The “rectangular part around the nozzle” is the heat-block. There are two cylindrical things inserted into this nozzle … the larger one is the heater cartridge; the smaller is the thermistor. The thermistor (variable resistor sensitive to thermal heat) tells the printer when the heat-block is at the required temperature and the heater cartridge is the thing that makes it hot.
It must not be allowed to be loose. This will result in a filament leak and that will cause other problems such as bed-leveling errors.
The extruder has a “cold” end and a “hot” end. The filament enters the “cold” end. There is a heat-sink and a cooling fan which is constantly blowing air through the heat sink when the printer is operating. This is to keep the “cold” end cold. It must not be allowed to heat up … the filament must not melt until it reaches the “hot” end or you’ll have issues with jams.
The “hot” end must be hot to melt the filament. To minimize heat flowing from the “hot” end to the “cold” end there is a gap to reduce thermal conductivity. The gap is called the “heat break”.
Here’s where the loose “rectangular thing” becomes important. The heat brake is a threaded tube. It threads into that “rectangular thing” (the heater block) from above. The extruder nozzle threads up from the bottom. The end of the “heat break” and “nozzle” meet in the middle of the heater block and they need to form a seal. If they do not then melted filament will ooze through the gap, through the treads, and result in filament oozing up through the top of the heater cartridge. This melted filament acts as an electrical insulator and will result in the bed-leveling (which relies on electric conductivity) failing to accurate level the bed.
The heat-block is soft aluminum … over-tightening can strip the threads (and this happened to my printer). But under-tightening can result in a leak. So you want this to be snug … but don’t over-torque it.
You’ll need a 7mm socket for a ratchet drive. You’ll need to heat the heat-block to around 280°C and then snug the nozzle while holding the heater-block square. (If i were to change out the nozzle then I cover the print-bed with a damp towel so that if the 280°C nozzle falls on the bed … it wont damage the PEI. Not that you are changing the nozzle … you just need to snug it in a bit.)
Be careful of the wires going into the heat-cartridge and thermistor on the side of the heat-block. You don’t want to damage those. As the Wicked Witch of the West says in Wizard of Oz … “These things must be done delicately.”
The wire going into the side of the heat-cartridge is solid-core wire. Braided core wire can bend easily. But solid-core wire will break. Be careful not to bend the solid-core wire.
If you’d rather not deal with any of this … LulzBot will rebuild the tool-head for you if you send it in. This isn’t covered by warranty so there would be a charge for it. But they’ll send the tool-head back to you in working order.
It’s a great printer and mine has been very reliable. But I did have an issue with a loose heat-block due to stripped threads … which is why I caution you to be careful as you fix this. It is literally the only issue my printer ever had.