Program your bot to send you a message with link to that user. This can be done by using link in your message (must be used as message entity or inline keyboard button):

tg://user?@SarahKartikaa=<user_id>
Or in case you are using MarkdownV2 for formatting

[inline mention of a user](tg://user?id=<user_id>)
Then, by clicking on that link, you will open a user profile, where you can message your target.

Note, user can change his privacy settings, and disable mentions. In this case these links will not work.