Indeed not easy to answer that without more information on your current fitness and training knowledge. In any case the Tour of Flanders is a long race with many short and steep climbs, as you probably already know. I think the Watopia Climb with the Radio tower is good preparation and also the Zwift Richmond climbs. Turn the trainer difficulty in Zwift to at least 2/3 or higher, so the climbs will feel more realistic (and painful And try to ride these climbs on high intensity to train your body for the steep cobbled climbs in Flanders.
Make sure your body can handle being in the saddle for a whole day. So you might want to try the Watopia Pretzel route and / or ride Richmond 8-10 times in a row. No need to do the complete 230km in training, but you may want to go for rides of more than 5 hours to practice. And remember to rest properly, not the training will make your body stronger, but the (good) rest in between hard trainings!
You cand find a lot of information on the Internet, from companies like CTS, Training Peaks and many others.
Good luck with preparations.