The reason why you have to hold the button down for your toilet to flush is because the flapper in the toilet tank is not opening fully when you push or hold down the button.
A toilet flapper not opening fully when you flush the toilet is often a result of a chain that is too loose or a chain that has too much slack.
You may need to adjust the chain that attaches to the toilet flush handle and flapper to make it shorter.
A damaged or misaligned flapper can also result in a toilet not flushing properly and may require you to hold down the flush handle or flush button for the toilet to flush.
Open the tank lid and try shortening the chain to the flapper and flush handle which usually fixes the issue.
If it doesn't fix the issue you may need to replace the toilet flapper if it's warped or worn out.
When the chain that connects the toilet flush handle to the toilet flapper is too long, it causes it to have too much slack and so when you push the handle to flush the toilet, the toilet flapper does not lift high enough for a full flush of the toilet.
Turn off the toilet water supply, unhook the chain and move the connection on the chain to the toilet flapper and toilet flush handle arm to shorten the chain.
Ensure that there's just a small amount of slack when the flapper is closed.
The flapper, that is the rubber or plastic dome that seals the drain hole from the toilet tank, may be worn or warped or even have some mineral buildup.
This can prevent it from lifting up high enough for sealing properly.
Check the toilet flapper for any damage and replace it if necessary.
You can also try twisting the toilet flapper to a higher setting if your toilet model allows, which increases the water flow.