Have you read the Handbook to learn how to adjust slurs? Double click if necessary to go into edit mode then use shift + right arrow to extend (shift + left to contract). Or select the whole range first then press S to add the slur in one step.
If this does not resolve your issue, please post the score you are having difficulty with and give precise step by step instructions to reproduce the problem.
Comments
Have you read the Handbook to learn how to adjust slurs? Double click if necessary to go into edit mode then use shift + right arrow to extend (shift + left to contract). Or select the whole range first then press S to add the slur in one step.
If this does not resolve your issue, please post the score you are having difficulty with and give precise step by step instructions to reproduce the problem.