Hi Chris,
1. Open TNT
2. Open your matrix
3. Open the tree file that you provided (constreeN1.tre)
4. Use this TNT command to export the tree(s) in nexus format: export - constreeN1.nex;
5. Open the nexus tree file with Mesquite
6. Use the following menu options in Mesquite: File > Export > Simple Newick/Phylip Treefile (using the name: constreeN1.nwk)
Done!
Cheers,
Steven