I would like to know if there is a specific prayer to ask for Parnassa. Also, which Tehillim would be most appropriate for this? Thank you very much

In the Tfilat Kol Pe Siddur there is a prayer for saying in Shomea Teffila. Also in most Sefaradi Siddurim you will find in Birkat Hashasnim a prayer for Parnasa. check also this answer. Bebirkat Hatorah, Rabbi Ro'i Margalit