If budget implementation is having difficulties or is being unsuccessful, what step you must do at a glance, and what else ?

I'd have a chat with the operations head.

Question needs little explanation.

Anyhow, my first action will be the analysis of the parameters used/based in the budget preparation. My other actions would be dependent of the results of the first action.

analysing

The first step will be to seggregate the actual and the forecast to go and to identify the trend of the variance of the actual vs the budget

The second would be to analyse variances to identify the reasons for the changes (if that is not already known) and revise the forecast with the current available trend wherever such trends are justified

The third step would be to seggregate the fixed and the controllable costs

The fourth step would be to put in place an effective monitoring and control process to ensure that the controllable/variable portion of the forecast does not exceed the revised forecast