Diagnostic: This is not a problem. It is the normal radial sidewall.
Indentations are quite natural on radial tyres (most tyres) and will not affect performance.
Your tyres feature one or more layers of fabric cord within the sidewall construction that run parallel to each other. (Steel cords are used within the tread.) Where the cords overlap, there is often slight indentation.
Symptom: bulge or bubble
Diagnostic: Tyre Damage that Requires Repair
Most punctures, nail holes or cuts up to ¼" confined to the tread, may be repaired by a tyre professional using industry-approved procedures.
An on-the-wheel plug-only repair is unreliable and dangerous because after a puncture, the inside of a tyre must be inspected.