There are several courses of action that are possible.
In some cases, you might reach out to the borrower and negotiate an adjustment of the terms of the note (this will help them stay in the property).
If the borrower is not in a position to resume making regular payments you may be able to negotiate a deed in lieu of foreclosure - a process whereby a borrower agrees to voluntarily hand-over the deed to their property to the lender instead of going through process of foreclosure.
In other cases, you can initiate a foreclosure and work with a realtor to sell the property.