its soo easy :-)
open your Instagram home page and select option "search" like this
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now just click on search bar for further options like this
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now you got multiple options to search about.
for example: Top , People , Tags , Places.
select option "Tags" LIKE THIS
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now write name of hashtage in search bar like this
click on hashtage option like this
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now a new page will open up with desired hashtage to follow up.
click on option "follow" like this
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now you are following your desired hashtage.
you will see all incoming posts in news feed.
thankyou.....