If you can swim, it is also good, but you must insist on swimming enough, for example, 1000 meters or more, and speed is not required. You can combine leg lifts with swimming in the swimming pool.
It doesn't matter if you don't do many push-ups. If you keep doing it for two weeks every day, you can do more.
In addition, you can do exercises at both ends at home, that is, lie on your back, and use your abdomen to drive your upper body and lower body up at the same time, which is very effective for increasing abdominal muscles.