Notes for Account field when creating expenses

Summary:

we have account field while creating expense item, which will get auto populated based on expense item type selected.

The requirement is that - at this account field, we need to have a short description - Notes as "Please update client and opportunity and activity". We have checked in sandbox for this field for customization, but we don't have short description box to give the required sentence in that field value.

how can we achieve this.

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