The first thing on the agenda is to impeach & convict, if there were enough patriotic Americans in Congress it should be possible this afternoon.
Then they can take their time to reverse all immunity granted by this President so all snakes can be rooted out.
Presidential pardon immunity is unreversable. There could potentially be a constitutional amendment on this, which is a super high bar, but even then the prohibition on ex post facto laws would only affect pardons going forward. It will be up to the states.