1998Subaru. Lights flash for app 30 sec. go off for 15 sec and come back on. Help

What lights? Can you give a few more details? Are you talking about the headlights, the parking lights, the lights on the dashboard? It would be helpful if you could describe the problem a bit more.

This is the factory alarm/keyless entry system. You need to cycle the locks with your keyless remote, or find the reset button above the control box (located under the dash, drivers side, far left, button is above the box in the wiring).

If it is not an alarm issue. Check and clean all of the grounds in the engine.

You either disconnected your car battery or had it replaced.

Like the one person above already stated...
Using your keyless transmitter, cycle the locks and it will stop or use the button on the wire harness from the control module around your steering column. Depending on who installed it, it is either still taped to the harness or it is located on the lower dash panel.