I would speak to Oxygen, who are good, and get a few probably about 20, they are cheap, replacement spokes of the right type. You may find that spokes on one side of the wheel differ slightly from the other side, Oxygen will explain.
I have two old Oxygen Emate city bikes from circa 2011 and have had spokes break in the rear motor wheels in both.
Now I am a bit of a bodger so you may wish to ignore the following advise.
Interestingly one rear motor wheel was a doddle to change a spoke and I could do it without removing the wheel or doing anything with the tyre at all. That was because the motor was narrow enough to remove a spoke and replace it screwing the replacement spoke into the old nipple and using a spoke spanner to adjust the tension without doing more than bend it slightly around the rotor of the brake.
The other motor wheel was a complete bugger, the motor was wider and I had to remove the wheel, tyre, brake rotor, and inner tube, and lever the rim tape aside to get at/replace the spoke nipple.
Not to depress you but you often find if one spoke breaks you might be in for a period of replacing spokes before you reach a point where they stop. However I have always managed to get to the stopped, or wheel stable point.
Wheel truing is a dark art and I take a simplistic approach. First assuming your wheel was reasonable true before the spoke broke, check them all and tighten any loose ones and generally and carefully increase by about a quarter to half a turn all the spokes on the wheel and then replace the broken one.
To get the spokes at roughly the same tension comparatively to each other as they were throughout the wheel I tend to tap them with a screw driver to get the tone of the spokes as a guide to their starting tension and increase each one by the same amount.
This is a pragmatic approach, has worked for me and enabled me to mend my own wheels but some more sophisticated advise may be along soon.
