As an OKR champion, identify champions at each level. These could be team leads/functional/pod heads to become partners in driving the process at their level.
Ensure every champion (leaders/managers) to fix a weekly check-in cadence and ask users to configure their reminder notification accordingly.
Make sure you have broadcasted that the OKRs on tool are a true reflection of an individual's work and they would be directly used as inputs in performance management.
Ensure cross-functional collaboration happens on tool and rather than offline creating accountability and actionability on what's happening.
Ensure your teams know how-to provide a great check-in and its value
A tool can never replace human touch. To make people feel more welcomed on the tool, make it mandatory to have profile pictures for every individual on the tool.