When you play with the baby, start putting their favourite toy in front of them, but a little out of their reach. This sounds mean, but it actually encourages them to make effort to move forward to achieve the desired object (why move if everything you want is always placed within reach?). Another suggestion to how to help baby crawl is to give the baby plenty of space to move around in. They may not be crawling yet, but they’re likely already rolling and some babies can roll all the way across a room (always supervised of course). Finally, if the baby makes it up onto all fours, put your hands behind their feet so they have a platform to push off from. It’s a bit like training wheels for a bike and helps the baby to feel more stable.
On the flip side, try to limit time spent in baby walkers, baby seats, baby carriers…basically anything where the baby is made to just lie there instead of being able to roll around on the floor. The more time spent practicing on the floor, the closer baby will get to crawling. Good luck aunty!