The next step is possible to do without the strings on, but if you want "live feedback" then you will put the strings back on.

If you aren't well acquainted in the restringing process, I recommend learning how to do so best in another tutorial as I am glossing over it.

Feed the strings through the hole in the bridge, like you did in step 1 but in reverse, be sure they are in the correct order

Tighten the strings and tune them, it will be necessary for them to be in tune for the aforementioned "live feedback" to work