With command line (recommended)¶
In a composer installation execute:
In a non-composer installation execute:
Without command line¶
Still in your old TYPO3 version, go to the "System" > "DB check" module and use the "Check and update global reference index" function.
Click on "Update reference index" to update the reference index. In case there is a timeout and you do not have CLI access (see above) you might have to run the update multiple times.