Use a wig cap, the kind used when cosplayers go to wear a wig, to keep your hair content, can buy in disguise stores or in internet.

If your headwrap no has velcro closure, put now around your neck.

Put lekku like a swimming cap.

Insert or remove stuffing to suit your head.

Here you can wear a tight bandana or use prosthesis glue according to your needs.

Prosthetic latex glue like Kryolan Mastix, Pros aide, etc. you can buy at costume/disguise shops or online.

I recommend Pros-aide, medic grade prosthetic glue. For me is the best. But others can work well for your skin.

Pros-aide works like contact adhesive: apply a little glue on the two elements to paste (lekku and skin), dry (have patience, I did not have and learned that it was best to wait), paste skin and lekku. Hold down for a few seconds.
To take them off to use adhesive remover/solvent, I think that alcohol or wipes cleansing also works, but better glue Remover.

Cut the excess of forehead if necessary.

Practice, experience is the best