N.H. Rev. Stat. Ann. § 479:10

If after such performance or payment, or a legal tender thereof, the mortgagee, being duly requested and having his reasonable charges therefor tendered to him, shall refuse or neglect to execute a release of his interest in the mortgaged premises, the mortgagor or person having his estate may apply by petition to the superior court in the county where the mortgaged estate or the greater part thereof lies stating the conveyance of the estate, the condition of the conveyance and the performance, payment or tender thereof, and praying for a decree of discharge or other relief.