Literally just start.

Find a YT video with an exercise bike instructor. Then try your best to follow. The point isn't to be perfect the point is to just peddle for the 20 to 30 minutes. Do this 3 times a week then after a month 4 times a week then after another month 5 times a week. Once you are doing a 30 minute bike ride 5 times a week, you can easily transition into other stuff. Like 3 bikes rides, and 2 jogs, and so on. The you increase length of time, 45 minutes, then 1 hour, etc. Set realistic goals, not everyone wants to use the free weights but attending exercise classes or completing daily 5 km runs are a realistic long term goal.