Doing Bantu knots, you can flat twist the leave out and taking the aid of perm rods in curling the leave out, could be another option for creating curls and kinks that will match your natural extension and helps to blend.
If all these fail –
You can take a pretty satin or silk scarf for tying the front portion of your head that will disguise your leave out. The scarf will look like a beautiful and stylish hair accessory. You can even use a matching closure with your extension and you will have no worry about blending. Blending as part of the installation is one of the most difficult maintenance problems with extensions. For that reason, many people opt for wigs, or full close sew-ins, or not wearing them at all. As the demand is always high, brands are also finding easy ways to rocking women with no effort. You can wear clip-ins on New year’s Eve or Thanksgiving and you will fairly hide your hide. You may avoid the blending problem because you fear it might look bad but with the aforesaid guidelines, you can make all the difference in the world. It doesn’t matter
if you have relaxed hair clip-ins or kinky ones.
Here is a step by step on Blending 4C Natural Hair with Clip-In Extensions

The most exciting reason for wearing
natural hair clip ins are perhaps the styling versatility. The benefits are many, whether you wear the clip-ins to achieve full puffs, or wear short bangs without shortening your hair, or achieve colors and highlights without any damage to your hair.
Step 1 –
Wash your 4c hair and condition it deeply. Do the usual of taking down the flat twist
Step 2 –
Take the 3 clips of the clip-ins and make a part section in the back. Your back parts need not be straight as they are going to get covered anyway. Make installation of the clip-ins with easy attachments.