You have av-event.jp as Nostro mentioned.
The process is quite simple as you go to the listed store and buy the specific title. You can get more benefits by buying multiple titles (from the same creator) which can give you 10sec extra shooting time and get one or two pictures together on your phone or on a Polaroid. Benefits are usually extended shooting time or getting one or two pictures together.
Some events could let you hug or hold hands with the actress if you bought one or two DvDs extra. Some would even take a step further and lick a lollipop near your ear or near your crotch etc. The ultimate blue ball teasing. Sadly this might not happen again in years as they dropped that ever since corona started and they still require you to wear a mask and keep a plastic wall between you and the actress.
Even so, you can get nice pictures and have a fun conversation and she might remember you next time you meet.
On either Twitter or an FC some actresses might announce an ofukai where you together with other fans spend time together to chat, drink, eat and play games, and sometimes karaoke, (don't expect anything erotic). Whether you think it's worth it or not is up to you as they are pretty costly and can cost between 30k to 60k yen and it usually isn't longer than 90 min to a couple of hours. There are many other fans who also goes there so there so don't expect many chances to talk your heart out.