Welcome to FS! You need to go back into the exercise diary. Click on the exercise you entered in error and in the box that pops up, you can then choose the down arrow next to the box that says "Increase" and choose "Reduce". Leave the time the same, as long as you want to delete this. You will then notice that beneath that it will say "Replace With" - and you can choose another default exercise.
At least that is how it works, due to the fact that I have it set up daily as 8 hours sleeping and 16 hours sitting. Then any exercise I do, I reduce the "sitting" time by how much exercise I do.
Hope this helps,
"Diet" is a four-letter word.
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