Convert VarChar to DateTime in SQL Server

Hello All, 

I Have database there i store value from datetime.now in date column but column have varchar datatype .

i want to get record last month to current date

but error convertin to varchar to datetime

please tell me how to convert varchar column to datetime to get record.

05/31/2018 10:45 AM

May 5 2018 10:45 AM

in this formate date inserted into logindate column and column data type is varchar so please tell me how to convert into date formate and get last 30 days data

thanks in advance