First I will check on multiple things like

Clarification Questions

1) Which rating -> (Driver Rating, Rider Rating, Play store ratings)

2) Is the BI tool which is showing rating is working fine? or the calculation of the rating is same or changed

3) The change is drastic, gradual , seasonal ?

4) the change is there globally or for a particular region?

Internal Reasons (missing)

1) Which platform IOs or android

2) The Tech infrastructure is working fine ? or there is any application crashes?

External Reasons (Missing)

1) Competitors like OLA running new discounts, coupons, scheme etc?

2) Any bad sentiment or bad PR in the society for example molestation by driver etc.

Consumer Behavior (Missing)

Is there any shift in the consumer behavior from covid like people now very skeptical about the safety and if the safety protocols are not followed by driver then also it can happen.

These can be included in the analysis to get more robust analysis.