Why won’t computer dual boot into Lubuntu

I booted from a live usb to install lubuntu in the side of windows in my Lenovo ideapad 1 14igl05 so I can dual boot but after the installation completed it boots straight back into windows and I try to look into the boot menu but lubuntu does not show up. I chose the replace a partition with lubuntu because I had a blank partition beforehand. I looked and it said that there was 20 go of space filled up in that partition so clearly it installed on the partition but then why can’t I boot into lubuntu or find the os in the boot menu?