To get started with the communication, it might be a good idea to first determine where are the bookings coming from. Is it direct bookings via the hotel's own website or is the majority of bookings coming from OTA's?
If you have guests booking their stay mainly via your own website, you might consider adding a visible section about online check-in and highlighting the benefits like no queues nor paperwork upon arrival, flexibility or digital key.
By communicating this digital transformation, you as a hotel are already building confidence in guests to use the product. It's important to mention, the more your guests hear and see about the online check-in throughout the journey touchpoints, the more likely they are to make use of it.
It needs to be in your best interest to inform potential guests of what you can offer that other hotels don’t.