Gather a lava source block
Gather a water source block
Place the lava and water so they flow into each other to create obsidian
Mine the obsidian with a diamond or netherite pickaxe
Build a frame using obsidian blocks
Make the frame at least 4 blocks tall and 5 blocks wide
Leave the corners optional
Fill the frame with a water source inside the frame
Place lava above or beside the water so it converts into obsidian in the frame
Use a piston and redstone to move lava and water into contact repeatedly
Use a dispenser with buckets to automate lava and water placement
Add a collection area to mine or gather the generated obsidian
Repeat the process as needed to produce more obsidian