What to do when Boot Manager of the multiple operating systems disappeared at the time of starting multi-boot – How to change OS starting order of Boot Manager

What to do when Boot Manager of the multiple operating systems disappeared at the time of starting multi-boot - How to change OS starting order of Boot Manager

What to do when Boot Manager of the multiple operating systems disappeared at the time of starting multi-boot – How to change OS starting order of Boot Manager

What to do when Boot Manager of the multiple operating systems disappeared at the time of starting multi-boot – How to change OS starting order of Boot Manager