First off welcome to the forum.Tzayad wrote:BUMP. Why? Because it is a serious question that should get an answer.
Second, not sure many on here will be able to answer you as that is an unusual route.
I believe you will have to fill out a form for retired federal law enforcemnt firearms certification with TCOLE. Here is a link to the form list https://www.tcole.texas.gov/content/for ... plications and this is the individual form https://www.tcole.texas.gov/sites/defau ... 0.14_0.pdf
Then you will have to certify with a firearms instructor. In Texas a LTC instructor can do the certification as long as it meets the TCOLE requirements. If you have a connection with your local law enforcement agency their instructor may also be willing to qualify you.
Once you have that completed you should be able to submit the application.
Hope this helps.