There is no need to run a tool to upgrade scripts from QTP 11 to UFT as stated in HP document [KM00316304][1]. As you have stated UFT will upgrade the script when it is loaded and saved again. The scripts are compatible as stated in [KM00208465][2] and forcing upgrade is not required. Older versions of QTP (9.x and older) required the HP Asset Upgrade Tool and the HP document [KM896902][3] give more details on this tool.
If you want to push the upgrade to all of the tests, then a custom VBScript to force the upgrade process have to be made. I have attached HP Document [KM200021][4] as reference how to do the upgrade that was used for QTP 8.2 to 9.0.
Below is listed document attached reference documents.
Document ID: [KM00316304][5]
Title: How to upgrade from QuickTest Professional and/or Service Test to Unified Functional Testing
Document ID: [KM00208465][6]
Title: What is the test compatibility between QuickTest Professional (QTP) / Unified Functional Testing (UFT GUI) versions?
Document ID: [KM896902][7]
Title: What is the HP Asset Upgrade Tool?
Document ID : [KM200021][8]
Title : Is there a tool that will automatically convert QTP 8.2 scripts to QTP 9.0
[1]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM00316304
[2]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM00208465
[3]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM896902
[4]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM200021
[5]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM00316304
[6]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM00208465
[7]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM896902
[8]: https://softwaresupport.hpe.com/group/softwaresupport/search-result/-/facetsearch/document/KM200021