Help with weight gain plan. Advice on routine!

So, I am currently working from home. no children.

I am working from 8-4. with a few times a week playing tennis at night and bible study.

I currently eat 4 weetbix in the morning, two sandwhiches lunch and a decent portion of dinner (usually something pasta or rice based.

I need advice on eating plan and working out plan.
Anyone got tips?