Garage Door section drops and I can’t close the door.

Panels are the individual pieces that form the garage door. Panels are typically made of wood, aluminum or vinyl.
When one of the panels drops or sags is usually caused by a cracked or severally bent panel. It is possible to repair this condition by installing one or more struts. Struts are supports usually made of metal or aluminum that attach to the inside of garage door running the entire width of the garage door. These struts give added support needed to keep the door from sagging or bending further, and will in most cases allow the door to function normally.
If it is the top panel that is dropping, it could also be a sign that the spine where the “J” bar attaches has or is failing and a new operator bracket may need to be installed.
The listed repairs could allow your door to last for many more years, but it could also be a very temporary fix with garage door replacement being needed very soon.
When considering adding struts and brackets to support the garage door panels, you must also be aware that this will add more weight to the garage door and you may need to change your spring or springs out to allow for the additional weight of the door.
It is possible in some cases to replace a single panel that has failed. First you would have to located the manufacturer name and model number of the garage door. You can look for stickers with this information on the inside of the garage door or on the sides of the panels. These stickers may or may not be on your garage door, and it can be difficult to determine the manufacturer or model number of the garage door even for garage door technicians. If the panel is damaged to the point that the panel needs to be replaced, many times it is easier and not much more expensive to replace the entire garage door.
*Note: Always use caution when working on your garage door. Garage doors can be dangerous and cause serious damage including death. Proper tools are required as are special skills when working on garage doors.