Missing value imputation is a very tricky question. In missing value imputation we have various methods which can impute the missing values, which also based on type of missing values we have in data. You can refer the link to know more about missing value types.
Here I am listing some methods which I used to impute missing values.
- Mean value imputation
- Median value imputation
- Use ML(single or multiple) model to predict missing values
Since I don’t know which tool you are using so you can refer this link to impute missing values in R.