The surface shown is almost like on  earth, just need a breathable atmosphere. Lichens may survive in these atmosphere.
If Mars is cold. They need to find a astroid rich in solid carbondioxide gas. They need to slam that ateroid into Mras so that % of carbon dioxide ( green house gas) increase which will eventually incraese the temperature .
Another way is to create genetically engenereed microbs which will use Martian raw material and release oxygen/carbon dixide/nitrogen gas into Martian atmosphere.