Hello,
Thank you for contacting Rank Math and bringing your concern to our attention.
Please note that some options are only available when you enable the Advanced Mode in Rank Math. If it’s not showing, you must have chosen to use Easy Mode.
You can follow the steps in this link to switch to Advanced Mode:
https://rankmath.com/kb/advanced-mode/
Once done, enable the Image SEO module in Rank Math > Dashboard

Hope that helps.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.