@mythxAHIR you can choose a specific name for an Excel sheet and you can opt to overwrite the whole Excel file or just the specific sheet if it already exists. If there are problems (within a larger jobs or loop you might be able to force the use of a specific name):
There is a free book and several videos for people coming from Excel to KNIME. You might want to take a look and familiarize yourself with the concepts behind KNIME.
From Excel to KNIME - written by Kathrin Melcher:
and there is this video by the author
KNIME and Excel - what you can and cannot do
An finally I have created a (large) collection abot a lot of use cases and examples about KNIME and Excel (some are advanced) that I have come by over the years - you might explore them as well