It’s all documented, and has been covered countless times in discord and the forums.
Here’s the link to the documentation: https://cyanlabs.net/docs/syn3updater/page/the-different-install-modes
Since your unit is not MY20, reformat is recommended: it’s cleaner and faster.
But, there’s a way of autoinstalling EU maps, without reformat. But be aware that this process takes “forever”.
This can be done because EU maps are not ESN locked, but the overall process is slow.
We have reports that it took 2-3 hours to update just the maps. More information here: 🔥🔥 2020 MAPS - EU (F10), NA (2.20) & ANZ (2.20) Maps added to Syn3 Updater 🔥🔥