How can I reset the combination and open my suitcase? I have forgotten the origanal combination.
Does the lock have the Travel Sentry logo on it?
Locks sold for the US market will have this logo along with a key slot for a TSA master key.
You can purchase a set of these master keys on eBay, Amazon, Wish, or many other shopping web sites around the world. The key with the code printed on your lock will open it. Or you can 3D print just the key you need, if you have a 3D printer.
Combination locks used on luggage are generally very poor quality, and not intended to do much more than keep out an opportunistic thief.
If you look somewhere like Youtube you will find countless videos that will show you how to open such locks. The exact method will depend on the quality of the lock and how many digits it contains, but could be as simple as simply rolling through all possible combinations (especially if the lock only has 3 digits).
To do it a little quicker (especially for 4 digit locks) you can normally apply pressure somewhere on the lock and feel when the lock falls into place. Again, the exact method will depend on the lock, so look on youtube to find one that is similar, and/or just follow the general advice given in these videos.
I recently found a 4-digit combination lock in the back of a rental car. Despite being a reasonable quality lock, it took me about 30 seconds to open by simply moving the rollers and feeling for them to latch.