Your approach shouldn’t be so much about having a conversation about deleting dating apps, it should be more so about having a conversation about where this potential partner is at emotionally and whether they want to keep this relationship going.
If they tell you that they are there with you emotionally, that is when you should bring up the topic of deleting apps.
This should be the natural progression of the conversation.
This way, it doesn’t feel like you are forcing them to do something they don’t want to. They are more likely to follow through on deleting their dating apps when they have been honest with you about how they feel and the potential they see in their relationship with you.