Is it permissible for a worshipper who stepped forward to switch on the microphone to return and complete his prayer with the congregation?

The worshiper should refrain from excessive movements beyond the actions of prayer, especially if there is no need for them, based on Allah's saying: (Guard strictly your prayers, especially the middle prayer; and stand before Allah with humility) and His saying: (Successful indeed are the believers, those who humble themselves in their prayers). The movement of operating a loudspeaker does not invalidate the prayer. If it is done out of necessity (such as a large number of worshipers and the imam's voice not reaching them), then the doer has done well. If there is no necessity, it is disliked, but the prayer is valid because it is a minor movement. Attention must be paid to not using loudspeakers outside the mosque due due to the disturbance it causes.