Mom and Pop commercial building leasing mistake

[Frank Nguyen]

Hi I have been helping my parents with communicating to their tenant about renewing a lease with a rent increase. My parents asked for a modest increase. I emailed the tenants and they negotiated an agreeable price with my parents. Both parties said they "can do this amount". No lease has been sent or signed yet for renewal. After some research on my own I found out my parents are very below market rent. Is it too late to change the rent amount? Should I just keep it the same?