What is the best short term forecasting to be used for user growth in the next 2-3 months? Trying to build an acceleration growth plan on excel but don't know where to start. I have a budget for every month recruitment but am flexible to increase my budget for the rest of the year so I can increase users.

Example:

I have a budget of 10,000$ for recruitment efforts each month on average and currently have 100,000 users on my platform but the goal is to increase total users by 20% in 3 months. I am willing to increase budget per month in order to gain more users. What is the best forecasting method to use for this? How would I go about building an acceleration plan?