Export calendar entries from phone to google account?

I've been working on and researching for a relatively long time. I have a Huawei P20 and I want to move all my calendar entries from the "Phone" account to my Google Account. However, I have not found a way to do this with my smartphone. Is there a (simple) possibility for this?

So I use the calendar app from Google… That's great. However, I have no P20, but a populous S6 with LineageOS…

I also use Google's Calendar app, which was already installed on my Nokia smartphone as I bought it.