For future reference, how do I reverse the leveling of character? For example, I have a level 8 character and for story purposes, I want to get back to level 3.

go into the character builder for the character, on the class tab, change the level in the drop down box from 8 to 3. It will pop up a warning 'are you sure'. You may want to make a copy of the character first too for reference if you need to level back up.

thanks for the advice on making a copy, I will do that, what about things like health and such?

I would just used the fix hit points rule, it will just be half the HD per level, round up, max at 1st, plus con mod at each level.

so start at level 1 and level up to 3 using the fixed hit points, that's your suggestion? I want to make sure I understand.

you don't need to level down to 1. The default HP method for D&D Beyond is the fixed HP rule, so it should just autocalculate correctly. If you had changed the "Hit Points Type" on the first character creation page to "Manual", just switch that back to "Fixed" and it will do the rest.

Edit your character by going back into the Character Builder.

On the Class page there is a drop-down showing your level. Click this and choose 3. A pop-up occurs to ask if you're sure. Click OK.

Go to the Home page of the builder. There is a switch for Hit Point Type. Is it Manual or Fixed?

-- Fixed.

You're done. Happy playing.

-- Manual.

Do you remember what you rolled for Hit Points when you levelled up to 2nd and 3rd levels?

-- Yes

Go back to the Class page. There is a button at the topfor"Manage HP". Click this. There is a popup containing a box for Rolled HP. Work out the max number of your class' hit die plus the combined total you rolled for levelling to 2nd and 3rd levels, not including any Constitution modifiers. Put this result into the Rolled HPbox, replacing whatever number it had before. Click to apply changes and you're done, happy playing.

-- No

Switch to Fixed. You're done. Happy playing.