Time Series Forecasting for Multiple Customers using one RNN

I have a product which has univariate and also multivariate time series data from multiple customers. I have variable amount of data available. Ranging between couple of years to couple of months. What I want to achieve is a model which takes as input training data from all my customers and forecast for 1 at a time. Thus utilizing patterns from all of them and then forecast for one customer at a time.

E.g.

Train:
Date        Customer  Variable
2018-01-01  A         10
2018-01-01  B         5
2018-01-01  C         13
2018-01-02  A         9
2018-01-02  B         7
2018-01-02  C         15

Predict:
2018-01-03  B         ?


Any help on how to formulate this problem and what would be the best model for this?