Find a convenient pool to swim. If you live in a condo, no excuses.
Can join clubs with swimming pools, though it will not be cheap.
Otherwise, swim in public pool if available.

Once venue is sorted out, its a matter of taking 30mins or 60mins to get started.
Start with 2 laps.. then 4, then 8..... slowly build up stamina.

If no suitable venue, may want to try something else like cycling, or jogging or even walking.