You don't have to eat meat, but you need to get enough protein, at least .7 g per lb of body weight but preferably around 1g. More than 1.5g is overkill. It helps to divide your protein goals by the number of meals you have and try to hit a per meal goal. There's no need to count calories or weigh your food or anything if that scares you, but it is good to look at serving sizes and protein content to get a rough idea.
You can try eating more beans and tofu. Bean pasta is a good hack. Seitan is really simple to make, especially if you've got a stand mixer and instant pot. You may want to consider getting some protein powder if you're struggling to get enough through food. You can add avocado and cocoa or nut butter and banana to protein shakes for some extra calories.
Well you also need to be eating at a calorie surplus of a few hundred extra calories per day, but that will ideally happen naturally if you focus on adding more protein to your existing diet. If you're going the protein powder route, you'll probably want to have it as an extra meal rather than a meal substitute. If you still struggle, you may need to track your calories to help you adapt.
YouTube can be a good source for some high protein vegan meal ideas. If you can do soy, TVP is a good option. If you can do gluten, chickmeat/seitan is good.