Hi Md Rasel,
It looks like the contract you're referring to was paused by the client. You can only add, edit, and delete time on an active contract in the current week’s Work Diary. You will not be able to delete logged time from the Work Diary of the paused contract. This is working by design.
Make sure to stop working on this contract and continue only after you can see that the contract has been resumed.
The screenshot you showed us looks like there is no delete button at the top of the screen.
If the contract is already CLOSED, you can not delete time segments.