Theren or Therein: How To spell?

The word Theren is misspelled against Therein, an adverb meaning "In that or this place, time, or thing; in that particular or respect."

Word contains consecutive vowels 'EI' in between alphabets ther & n is misspelled as 'E' as letter 'I' is phonetically ignored
Wrong Spelling:  ther-e-n 
Correct Spelling:  ther-ei-n 
Explore spell check of Therein to spell without errors.