It's very positive you've recognised so quickly there's an issue and are willing to change.
Current guidance is to refeed quickly, hence 3 meals and 3 snacks, a daily calorie guideline of 2500 + 1.5-2 litres of fluids (not carbonated). It is painful though, you will feel bloated - a hot water bottle will help. Your stomach is stretching.
If you don't feel you can manage that, then build up to 3 meals first.
Use calorie dense food eg if you can only eat a tuna sandwich, use seeded bread and full calorie mayo with the tuna. You're looking for extras that are easy to add - cheese on top of your pasta, cream in your coffee instead of milk, plenty of oil when cooking, butter on your bread.
Calorie rich drinks - fruit juice instead of diet soda, milkshakes, hot chocolate with milk. There's meal replacement drinks which have 500 calories in a bottle - if you can't manage a full meal, replace the lost calories with this drink.
Contact BEAT helpline, it's open weekends too. And they have online guidance via The Pod and other weekly support sessions.
Your willingness to address this is very positive, keep hold of that. It's ok not to be perfect - if you shoot for 3 meals tomorrow, but manage 1.5 and some high calorie drinks, that's progress on today. Focus on the progress you are making.
Best wishes to you x