Black patches on my avocado

[Chandramohan]

What could be causing these black patches on my avocados ? What is the remedy?

[Capt Ram]

Hard to say by the picture but I've had that happen to avocados that were left on the tree too long

[Chandramohan]

These are immature.

[pineislander]

Check anthracnose. I see that the infection is near the bottom of fruit which is logical for rain spread infections. Hopefully you know when they are ready to ripen. Often anthracnose appears post-harvest. Avocados don't ripen on the tree you might try picking and watching for a week or so.
https://www.ctahr.hawaii.edu/oc/freepubs/pdf/pd-58.pdf