I understanding that once non-eea national gets a family permit, they need to travel to the UK within 6 month and apply for 5years residency card whilst in the UK. Non EEA nationals do not get pre-settled letter with reference number (as given to most EU citizens residing in the UK) within 48hrs ...

I am a non-eea citizen looking to join a EU national in the UK who is on pre settled status. Can I switch to EUSS while I am travelling to UK on a tourist visa or do I need to apply for EUSS family permit?