Sure! This is actually pretty easy to do.
Please log into VRChat with your Steam account. Open your quick menu, then select Settings. Near the bottom of that menu, you'll see a button to "Upgrade Account". Click that and follow the instructions on the screen to merge your accounts.
Please note: If you have favorite avatars or worlds on the VRChat account that you are merging your Steam account into, the merge will ignore the favorites on the Steam account.
In other words, it is best to merge your Steam account into a new, blank VRChat account.