I have never used Findtail, but you can trim poly-A tails with Cutadapt, see https://cutadapt.readthedocs.io/en/stable/recipes.html#trim-poly-a-tails

I am sorted of confused by the use of the word internal priming. Usually that means that sequence adjacent to homopolymer-tracts of A within mRNA will become enriched due to the polyA-based random priming (used for example in mainstream RNA-seq library preps). So you will have reads enriched in sites that are relatively far from the polyA tail. To remove these you need to identify them genome-wide.

Trimming polyA-tails is not super necessary for aligners that do softclipping but otherwise you can use a trimming tool like the one suggested by @sheikmike