If the previous editorial decision was C (revise & re-review) or D (major revisions & re-review), the paper will be sent for re-review to the original reviewers, together with your responses. As a result of this, you may receive a further round of comments from the same reviewers.
It is JMIR policy to avoid assigning new reviewers in round 2 (3, 4, ...). If reviewers from the previous round are not available (no response or decline to re-review), then it is the task of the editor to evaluate if the comments have been addressed satisfactorily.
If the previous editorial decision was B (minor revisions), only the editor will see the author responses and will make a decision based on them.
It should take at least a few weeks for re-review and the editor to make a decision after your revision is submitted (if the previous decision was B (minor revisions), then the timelines may be shorter). Note that the time it takes for an editor to make a decision on your revision may vary depending on the editor's workload and the time of year.