Board Thread:Game Help/@comment-32799778-20170807212639/@comment-26440657-20170808104535

Why would you flood it with lava? You should've known it would be a problem...

You could try getting a Bottomless Water Bucket and pour water on the lava and then mine the obsidian or you could mine the floor so the lava goes there. That's all I could think of, if other methods exist, youtube probably has tutorials.