I have an example dataframe that has a column which stores 3 letters of the alphabet per row. The dataframe also has 2 additional columns: date and colour:

```
Alphabet       Date   Colour
  ABC    2018-09-10   green
  DEF    2017-06-11   red
  GHI    2016-05-12   blue
  JKL            NA   yellow
  MNO            NA   orange
  PQR       Unknown   brown

```

Some of the dates are missing / unknown in this dataframe. I have another dataframe which also has a alphabet and a date column. This second dataframe includes the dates for the missing dates in the first dataframe:

```
Alphabet       Date   
  JKL    2017-06-07  
  MNO    2018-08-03   
  PQR    2019-10-07
  STU    2019-11-08
  VWX    2019-12-08   

```

I want to fill in the missing dates from the first dataframe by matching the Alphabet records from both dataframes and then insert the dates from the second dataframe into the first dataframe. 

Desired output:

```
Alphabet       Date   Colour
  ABC    2018-09-10   green
  DEF    2017-06-11   red
  GHI    2016-05-12   blue
  JKL    2017-06-07   yellow
  MNO    2018-08-03   orange
  PQR    2019-10-07   brown

```

Any help is appreciated.