There are two parts to the FMM Immigration Form: the Entry Form and the Exit Form. The Entry Form is taken by the immigration official at the Mexican Border, who stamps the Exit Form.
This second part of the FMM must be kept by the visitor until they leave the country.
If this part of the FMM is lost, stolen or significantly damaged in Mexico itself, international visitors should take the following actions:
Go to the nearest Police Station and file a report of the loss or theft of the Mexico Tourist Card.
Locate the nearest Mexican National Institute of Immigration (INM) office with the police report and request a replacement FMM
Alternatively, travelers can wait until they leave the country and simply pay a fine of around $40USD for failure to present a Mexico Tourist Card.