Hi dear, to motivate someone to exercise its purely their personal interest.. unless they're willing to workout u cant force someone to follow a routine. So u can explain the pros and cons to them and let them take their own time to decide
I feel it's really important that the type of exercise should first be enjoyable enough and not feel like a chore or punishment. For example, running for some may be their preferred form of exercise that they genuinely love doing, while others would hate it therefore not be motivated to do it at all, but instead find out that cycling is really fun for them. Finding the right kind of exercise for you that makes you feel good first and foremost is the first step! Exploring the potential benefits of continuing this preferred form of exercise and how valuable those would be to you should allow for motivation to come naturally.