Killing governor in The Colony's God mission is pretty complicated in Assassin’s Creed Liberation. The mission is in the first sequence of the game and might prove to be a bit challenging. Especially if you are trying to reach 100% synchronization, which specifically requires that the governor would be killed with a musket.
The mission allows you to choose your own way of entering the governor’s mansion, so you can dress either as slave or a lady, both these outfits will allow you to go through the main gate (as a slave you will have to carry a crate to blend in). However, the outcome of the mission must still be the same, you have to kill the governor, preferably with a musket. Main tip in achieving this is to fight well. Ridiculous? Maybe. But that is what you have to do. Block counter, take the musket away from the guards and shoot the governor.
There are several ways to kill the governor in AC Liberation, so if you’re stuck feel free to check out the video examples of both the Lady persona and the Slave persona completing Assassin’s Creed Liberation The Colony’s God mission, maybe it will give you ideas on how achieve the goal.