I think you are confusing things. There is iTunes the application, which is a piece of software, and then there is your local iTunes database which is stored in the iTunes Library.itl file mentioned in the first post.
If the application needs reinstalling then read on:
For general advice see Troubleshooting issues with iTunes for Windows updates.
The steps in the second box are a guide to removing everything related to iTunes and then rebuilding it which is often a good starting point unless the symptoms indicate a more specific approach. Right-click on the setup file and run the installer as administrator. In some cases you may also need to disable any non-Microsoft anti-virus software while installing.
Review the other boxes and the list of support documents further down the page in case one of them applies.
The further information area has direct links to the current and recent builds in case you have problems downloading, or want to revert to an older version if the current one won't work properly for you at the moment.
Your library and device backups should be unaffected by these steps but there are links to backup and recovery advice should it be needed.
If you had installed, for example, iTunes 12.7 and decided that you didn't want it, and so removed it and reinstalled iTunes 12.6.3 instead then the initial warning message is to be expected as older versions of iTunes cannot read libraries created by newer versions. In such a case you would take an appropriate .itl file from the Previous iTunes Libraries folder inside your main iTunes library folder (usually inside User's Music) copy it up into the iTunes folder and rename the library files so that one takes the place of other. If you have no older .itl files to revert to then delete or rename the one that you do have which allows iTunes to create a new empty library.
tt2