This is easily attainable in the tutorial world, head up the stairs and on your right is a potions room with all the tools you'll need.
Firstly grab everything from the chests then with the glass bottles equipped press R at the cauldrons to turn them into water bottles (3). Now press L onto the brewing stand and place your 3 water bottles into the stand and place Nether Wart at the top and let it brew.
You should now have 3 Awkward potions, now place Magma Cream at the top and let it brew again which will give you your Fire Resistance potions. Grab them and head over to the room with the anvil opposite.
Drink the potion and break the cobblestone in front of the lava and swim!
Here's a video