First, install front brakes on the bike. Even cheap rim brakes with KoolStop pads would be better than nothing.
You need them, even if you have regen braking--if the battery is fully charged, for instance, regen doesn't work. (or if it does, it could damage the battery by overcharging, if the battery's BMS doesn't shut the battery off to protect it). Or the controller could fail (for whatever reason, even unrelated) and then you'd still have no front brake.
"low level" probably just means that you connect the ebrake wire to ground to activate the ebrake.
Normally regen is already enabled on most of these controllers, but if it doesn't work, there may be pads you can connect (with a wire or solder bridge) inside the controller to enable it. Otherwise you'd have to program it with controller-specific software (usually not available).
If you need to solder pads or jumpers inside to enable things, then there are threads around here about various controllers that may help, depending on which type yours is (there are at least hundreds, thousands, or more different designs). Here's one (that links to others)
https://endless-sphere.com/forums/viewt ... =2&t=68501
BTW, in reference to "level" of brake: "high level" brake usually means you connect hte ebrake wire to 12v to activate the ebrake, and sometmies this engages a different mode than "low level"; for instance, LL might engage regular regen, while HL might engage "EABS", which actively brakes the wheel by powering it in the opposite direction, rather than just tapping power away from the wheel into the battery.