DateTime String: "20/08/2020 08:15:55"
Format String: "dd MM, YYYY HH:mm:ss"
Given a DateTime string and a Format string, write a Python program to convert the given DateTime string to the specified format.
In order to convert the given DateTime string to the specified format using Python, we need to use the datetime module. Here's a program that accomplishes the task:

```python
from datetime import datetime

def convert_format(date_string: str, format_string: str):
    # Convert DateTime string to a datetime object
    date_obj = datetime.strptime(date_string, "%d/%m/%Y %H:%M:%S")
    
    # Reformat the datetime object using the given Format string
    # First, change the given Format string to the format codes used by the strftime function.
    format_codes = {"dd": "%d", "MM": "%m", "YYYY": "%Y", "HH": "%H", "mm": "%M", "ss": "%S"}
    for k, v in format_codes.items():
        format_string = format_string.replace(k, v)
		
    new_date_string = date_obj.strftime(format_string)
    return new_date_string

date_string = "20/08/2020 08:15:55"
format_string = "dd MM, YYYY HH:mm:ss"

new_date_string = convert_format(date_string, format_string)
print(new_date_string) # 20 08, 2020 08:15:55
```

In the above program, we first convert the given DateTime string into a datetime object using the `strptime` function. Next, we reformat the datetime object using the given Format string by first converting it into the format codes used by the `strftime` function. Finally, we use the `strftime` function to generate the new DateTime string in the specified format.