Lynn's RP Stuff

First thing, go ahead and update your mods. This tutorial is for fixing already broken blocks. This works for any mod which has broken or been removed.

You will need Creative Mode. Type /op self in chat, and then press O to enter creative mode. If you have stuff in your inventory you should put everything in a chest for now.

Press Tab to open the inventory and at the top there is a search bar. Type "selection" and give yourself a Selection Tool.

This next part is for replacing blocks that did not correctly update. If you just want to remove broken blocks without replacing them, skip this paragraph. Find any broken block and stand on top of it. Type /block get ~0 ~-1 ~0 (If the hitbox of the block prevents you from being directly on top, you can stand or fly above the hitbox, and change the -1 in the command to the number of blocks below you it is) This will tell you the internal name for what the broken block was so you can replace it. You can use the name to search for a replacement item from the inventory.

You can now remove the broken block. If it's a single block you can just break it, but if around the block there are invisible faces, select the area with your selection tool so that it covers all the empty blocks around the invisible faces. You can press L while holding the Selection tool for more detailed instructions on using it. Type /clear, to remove all blocks from inside the selection. Press the Delete Key to get rid of the selection box(sometimes hitting delete doesn't work, relogging fixes this)

If you have Invalid Items in your inventory or chests, you can hover your mouse while in creative mode to see the internal name of the item. You can replace the items from the creative inventory, and then drag the items onto any item in the creative menu to destroy it.

Repeat as needed. You can press O again to leave creative mode.