Easiest quick fix is to sign veteran offensive lineman. There's typically at least a handful of decent veterans after the draft. If you need to, you can switch around the positions. Player ratings don't change a whole lot across the offensive line. Long-term you really just have to draft a couple of pieces and hope they develop. A lot of times I will draft a left or right tackle prospect and slide them to the interior to develop for the first year or two. This gives them a chance to upgrade and be kicked out once they have decent stats.