You can tame a Stryder by "hacking" it with a substance called Mutagel. Additionally, you have to finish a certain number of tasks or missions. You won’t need to complete more than 51 missions to tame one Stryder. The amount of Mutagel and the number of missions you need will go up as the Stryder’s level increases. Also, each Stryder has set rigs, which can’t be crafted or swapped out.