My father wanted to sell his Breitling Navitimer watch however he lost the cert that came with the watch.
How do I get it appraised to sell the watch?

Read the faq:
https://www.breitling.com/my-en/service/faq/

Get a Breitling digital passport for the watch.

To authenticate your Breitling watch, it must be sent to one of our Breitling Main Centers. Begin by sending your watch to any Breitling service center or by bringing it into a Breitling Boutique, requesting a Certificate of Authenticity, and your watch will be passed on accordingly. Fees and return times will vary.
An authentication includes the analysis of the watch and the delivery of a Certificate of Authenticity. If non-compliant parts need to be exchanged to return the watch to its original condition, these will be invoiced separately.
Breitling service centers and boutiques do not assess the value of your timepiece. For this kind of information, we suggest our online estimation tool available in the USA and Europe by registering, creating an account on Breitling.com and claiming your Breitling NFT. This tool can be used for most watches produced after 2013.