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Howdy @BrendaKay, welcome to the forums! 
If your profile's stride length was not subscribed to your profile; your past steps were estimated on your height and gender. However, if you had a previous stride length added to your account; unfortunately these steps cannot be recalculated for your raw step data (steps only detected by your tracker).
Nevertheless; if you had Manual logs or MobileRun logs, you can delete these logs and create individual manual logs for these past activities. I don't recommend this because there's some data that could prove relevant in your caloric calculations (like your heart rate, height, gps maps, etc) whilst a manual log is only calculating the steps and distance.
Hope this answers your question; happy stepping! 
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