Note payment tracker

[Mark Gibbs]

Hi BPer's I've gotten myself into a situation that I need some help with. Short story, I signed a tenant to a commercial space lease and that tenant has notified me he is not able to complete the terms of the contract. When I initiated this lease I had the tenant sign a personal guarantee for certain portions of the lease should he fail. I am now needing to execute on the personal guarantee. 

The tenant has agreed to sign a deed of trust against his personal property and a note to pay the amounts due. This isn't a huge dollar amount but I will need to keep track of payments against the principal with interest calculation and apply additional payments toward principal. I can't justify handing this to a servicer and I am not sure they would even take it. 

Can anyone direct me to any online tools for tracking this type of debt? Private message me if preferred.