Assuming that this is Post Categories, the easiest thing is to hide the All Categories with Custom CSS.
.sf-field-category .sf-item-0 {
display: none;
}
But, if it is a custom taxonomy, the name would be different, so you would need to substitute the class .sf-field-category
with whatever the taxonomy you are using has as a class in our form.
Is ‘This months featured blogs’ a category already in the list? If it is, you may need to re-order the list of terms. This is not so easy, but would use this filter (there are many other snippets of code using this filter in our forum):
https://searchandfilter.com/documentation/action-filter-reference/#filter-input-object
Snippet search:
https://support.searchandfilter.com/forums/search/function+sf_input_object_pre/
But, what is not possible would be to pre-select that option on loading the form for the first time. I think that feature will arrive with V3 of our plugin in a few months time.