same as the title........

1. Join a level that you have building permissions in.
2. Navigate to the 'Decoration tab'
3. At the bottom, there should be a block called 'Item mesh'
4. Place it in.
5. Go to 'Shop' on the bopimo! website.
6. Go to Shirts.
7. Look for whichever shirt you wish to use, for example, this is specifically designed for doing this: https://www.bopimo.com/items/5060

8. Copy the final part of the URL(the id)
9. (i hope you didnt close the client) In the bopimo! client tab, Click the item mesh.
10. Click the gear icon on the top.
11. Search for the "Item ID" setting.
12. Click it and Paste the ID that you previously copied

If you want to make your own decal, Heres how!

1. Firstly, I recommend using a platform like scratch.mit.edu, just not something like MS paint. All it needs is for you to be able to make images with invisible backgrounds.

2. Open the bopimo! Website, Go to the Shop, Click the + Icon in the top right corner(keep this tab open for later)
3. Click template. Right click the shirt template icon. Click Save image as... and now save the PNG as something called 'Shirt template' Despite it not mattering.
4. Enter the program you want to use to make your decal.
5. Import 'Shirt template' Or whatever you named the PNG.
6. Remove the colorful cube-like shapes that are marked with letters such as F, B, T, L, R. EXCEPT the big purple square in the middle(ish) marked with F.
7. Put whatever image you want in place of the purple square.(Most likely you'll want it to have a transparent backround, so instead you can just remove the purple square, JUST REMEMBER WHERE IT WAS.)
8. Export the shirt you made. Name it something you'll remember like 'DecalTest123' Head back to the bopimo! website tab named 'Create Item - Bopimo!'
9. Click 'Upload Texture.'
10. Search in 'downloads' or wherever you exported the image to.
11. Double click it to choose it. Give it a name + a description. Set it to free, offsale, or onsale, Your choice! If you choose onsale, Put how much you want it to be worth. Once you're done, click the 'Create' Button!
12. Wait for the shirt to be accepted, patiently. This is the longest step(probably)
13. When its accepted, Use the other guide i posted to use the shirt as a decal!