Presuming the house is resting on a footing or a slab, the framing can be raised and shimmed up. However, if the slab or footing is sinking, the supporting structures may have to be underpinned or rebuilt.

You support the house close to the corner, dig a hole for a piling or support column, pour concrete in the hole.

Put the jack on or in the hole (depends on the size of the jack)

THEN you jack up the house so it's level, which takes quite a while because you have to let it adjust to its new shape)

THEN you leave the jack in place and dig out to make a proper footing for the rest of that corner.

If 1 corner has sank, all others will eventually follow in my experience. Best to jack and rebuild where there are not any basement foundation walls.

Has the root cause of the settling been discovered? Sad to remedy only to find a reoccurrence in a few years.

First thing you really should do is have an engineer inspect so you know if there is a chance of the entire structure failing!

There was once a street of early 20th Century "bargain" homes not far off the downtown here. The only catch: they all leaned in different directions, as they were built on a former landfill. So I demurred. Big mistake. Today, the entire multi-acre one-time garbage pit sports a massive mid-rise development.