If the timing belt has too much slack in it and the marks on the crank and cam gear are out of alignment, honestly you should address that first.
How old is the belt?
If it's slipped one tooth it'll run like garbage, if it's slipped two teeth it won't run at all.
But, if you're not wanting to pull the belt, just do a compression test, if the numbers are healthy then you know the timing is basically OK.
Either way, adjust the belt tension, turn the crank (clockwise) a tad to make sure the belt has all its slack on the tensioner side, then release and re-tighten the tensioner bolt to set the tension. You don't need to remove the timing cover to do this, you just remove the rubber bung on the front of it, this gives you access, just make sure not to push the bung right through the cover when you're reinstalling it 😅